Reduction of DNA primase activity in aging but still proliferating cells

✍ Scribed by James M. Collins; Annie K. Chu

• Book ID: 102884551
• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 854 KB
• Volume: 143
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041430107

✦ Synopsis

The basis of the well-known decline in cell proliferation with increasing passage number of human diploid fibroblast-like cell cultures is not known. It has been found that D N A synthesis was deficient in the remaining but still proliferating cells, but when appropriate corrections reflecting the remaining dividing cells were made, the amount of D N A polymerase a bound to nuclear matrices was normal [Collins and Chu: lournal of Cellular Physiology 124: 165-173, 19851. In the present study, the declining percentages of S-phase and dividing cells were determined to provide better estimates of functional culture age than passage number. The amounts of D N A polymerase a and D N A primase activity were determined in cell lysates, permeabilized cells, and bound to nucleoids, which are residual nuclear structures similar to nuclear matrices except that n o DNasedigestion step is employed. As expected, IMR 90 D N A synthesis declined with age, even after corrections for the declining numbers of proliferating cells. D N A polymerase a and DNA primase activity in cell lysates, permeabilized cells, and bound to nucleoids declined with increasing age. However, after appropriate corrections for the declining fraction of proliferating cells, the only activity that declined was that of D N A primase bound to nucleoids. Thus, a decrase in the binding of D N A primase to the nuclear site of D N A synthesis may account for the decreased D N A synthesis in aging but still proliferating cells.